[ID3 Dev] RVAD -> RVA2

[Jud White]

n-bit:
dB = value/(2^n - 1) * (6dB * n)
16-bit:
dB = value/(65535) * (96dB)

where 'value' is an RVAD 2.3 adjustment.
The '6' constant is 20*log10(2) (which is ~6.02)

I think.. maybe I'll post on Hydrogen Audio

----- Original Message -----
From: Jim [mailto:jmartin92 at comcast.net]
To: id3v2 at id3.org
Sent: Thu, 18 Jan 2007 16:50:47 -0500
Subject: Re: [ID3 Dev] RVAD -> RVA2

So then for the value to db conversion it would be:

    db = 20 * log10 ( 1.0 [+ or -] value/65536) where the + or - would be
decided by the increment/decrement flag??

----- Original Message ----- 
From: "Ben Allison" <benski at winamp.com>
To: <id3v2 at id3.org>
Sent: Thursday, January 18, 2007 4:12 PM
Subject: Re: [ID3 Dev] RVAD -> RVA2


> This would correspond to value/65536  (-12850/65536 = 0.196,
> -26471/65536 = 0.404)
>
> Mitchell S. Honnert wrote:
> >
> > For what it's worth...
> > When I implemented the RVAD frame for my ID3 library, I found the
> > iTunes implemented it, so I used its implementation as a guide.  (In
> > spite of iTunes' mangling of ID3v4.)  The iTunes UI has a "Volume
> > Adjustment" slider which goes from -100% to +100% with tic marks at
> > every 20%.  A -20% in iTunes results in the Right Volume and the Left
> > Volume fields being "Decrement 12850".  -40% was "Decrement 26471".
> > At the time, I scratched my head a bit, wondering why the frame would
> > need these large values, but I didn't really delve into it too far.
> >
> > - Mitchell S. Honnert
> >
> > ----- Original Message ----- From: "Jud White" <jwhite at cdtag.com>
> > To: <id3v2 at id3.org>
> > Sent: Thursday, January 18, 2007 2:29 PM
> > Subject: Re: [ID3 Dev] RVAD -> RVA2
> >
> >
> > Turned up some information, but still need the gaps filled in.  Please
> > help, anybody :)
> >
> >> From the ID3v2.3 spec on RVAD:
> > The 'bits used for volume description' field is normally $10 (16 bits)
> > for MPEG 2 layer I, II and III and MPEG 2.5.
> >
> > One interpretation is the adjustment data is directly related to the
> > way 16-bit audio is stored (let's assume we're talking about 16-bit
> > for simplicity).  I personally don't see any other possibilities for
> > interpretation on this, although I'd be fine with asking any major
> > implementor what they did.  Nice to see Winamp fixed their Compliance
> > issues, maybe they could shed some light on RVAD (if they use it).
> >
> > What I turned up (probably most of you know this already) is that each
> > bit in digital audio is capable of representing roughly 6 dB
> > (specifically, 20*log10(2) dB).  Therefore, 16-bit audio is capable of
> > representing 96 dB. Initially I was confused - how can 1 bit represent
> > 6dB, and even if it does how does it increase linearally instead of
> > exponentially?  Quantization, or in other words, the curve isn't a
> > curve it's a lot of little steps.  As you increase bits not only does
> > the max dB you can represent go up but the steps get smaller.  Ok, I'm
> > sure most of you know this, I'm writing to help myself understand. :)
> > If someone wants to flesh out this description please do.
> >
> > Here's a good article: http://www.tc.umn.edu/~erick205/Papers/paper.html
> >
> > My take:  RVAD/RVA adjustment is likely implemented the same way as
> > n-bit audio.  If it is, then dB = value/(2^n - 1) * (6 * n).  e.g., in
> > 16-bit audio: dB = value/65535 * 96.
> >
> > Jud
> >
> >
> >
> >
> >
>
> --------------------------------------------------------------------------
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> >
> >
> >
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